How are the halves of the brain connected?

How does the brain work?

The brain needs to be constantly supplied with enough oxygen and other nutrients. That is why it is particularly well supplied with blood. Each hemisphere of the brain is supplied with blood by three arteries:

  • The anterior cerebral artery (Arteria cerebri anterior) supplies the tissue behind the forehead and in the area of ​​the vertex.
  • The middle cerebral artery (Arteria cerebri media) is important for the side and more internal areas of the brain. The anterior and middle cerebral arteries branch off from the internal carotid artery.
  • The posterior cerebral artery (Arteria cerebri posterior) supplies the back of the head and the lower part of the brain as well as the cerebellum. It is fed with blood from the vertebral arteries.

Before the three arteries move into “their” brain regions and branch out into smaller branches there, they lie close together below the brain. Here they are connected to one another via smaller blood vessels - similar to a roundabout. There are also connecting paths between the individual arteries at more distant locations. This has the advantage that circulatory disorders in the brain can be compensated to a certain extent: if, for example, an artery branch gradually becomes narrower, blood can still flow into the affected brain area via these "detours" (so-called collaterals).

The finest branches (capillaries) of the cerebral arteries release oxygen and nutrients from the blood to the brain cells - but they are less permeable to other substances than comparable blood vessels in the rest of the body. Experts call this property the “blood-brain barrier”. For example, it can protect the sensitive brain from pollutants dissolved in the blood.

"Used" - that is, low-oxygen - blood is transported away via the cerebral veins. They direct it into larger blood vessels called sinuses. The sinus walls are reinforced by hard meninges, which stretch the vessels at the same time. This keeps them permanently open and the blood can always flow unhindered into the neck veins.